The present invention relates to an airbag which functions to protect passengers in a vehicle during a collision.
Airbags have become widely used as safety devices to protect passengers traveling in a vehicle. Besides airbags designed for safety of the driver, specific locations inside a vehicle where airbags are installed have also increased to include airbags designed for safety of passengers, for protection in case of side collisions, as well as rear-seat airbags.
As the number of airbags present as well as the specific installation points in a vehicle increase, so does the need for airbag devices which are lighter and smaller. In response, inflators, which are the heaviest component of an airbag device, have been designed which are smaller and lighter, and which use less chemical agent or gas than previously. However, with a decreased amount of chemical agent or gas, there is an accompanying decreased amount of gas that can be used to inflate an airbag. And usually, there are one or more round vent holes in an airbag by which gas exits, and gas prematurely escapes an airbag by the vent holes even during the initial inflation stage of an airbag. In order to make optimal use of the limited amount of gas available, airbags have been designed where the vent holes are at first sealed, and open to let gas escape when the pressure inside the airbag has increased to a certain level.
Japanese Patent Provisional Application (Heisei) 8-268214 discloses an airbag which has a reinforcing sheet having a C-shaped cut about an outer circumference of a vent hole which the reinforcing sheet covers. Japanese Patent Provisional Application (Heisei) 7-205738 discloses an airbag having an area around a vent hole being brought together by folding and held together by stitching, the stitching being torn apart by pressure inside the airbag reaching a certain level. Japanese Patent Provisional Application 2002-59803 discloses an airbag having slit-shaped vent holes which are covered with an adhesive agent, the vent holes becoming opened once a predetermined internal pressure has been reached inside the airbag. Therefore, the airbags disclosed in these documents are able to make effective use of gas provided by an inflator by maintaining vent holes in a sealed or closed state during the initial inflation stage.
Also, in order to regulate the projection distance that an airbag inflates toward a passenger and realize desirable inflation characteristics, there are airbags which employ various means to regulate the inflation shape of an airbag, for example, a tether or strap. Japanese Patent Provisional Application (Heisei) 6-298025 discloses a driver's airbag having a front panel and a rear panel which are held together by an adhesive agent, the adhesive agent being melted by the heat of gas filling the bag to allow final inflation of the airbag. Japanese Patent Provisional Application (Heisei) 8-156730 discloses an airbag which has inflator side material and occupant side material held together by stitching which breaks apart once the internal pressure of the airbag has reached a certain level.